This invention relates to a one-reel magnetic tape cartridge for use in a computer or the like.
As a backup medium for a computer memory, there has been known a magnetic tape cartridge comprising a thin rectangular cartridge casing formed of upper and lower halves fixed together by screws or the like and a single reel which is housed in the cartridge casing for rotation and around which a magnetic tape is wound.
When such a magnetic tape cartridge is loaded in a recording and reproducing apparatus, a drive member of the apparatus is engaged with engagement teeth on the reel exposed through a circular opening formed on the lower half of the cartridge casing at the center thereof and the magnetic tape wound around the reel is drawn out from the cartridge casing into a predetermined position on the tape running path by a tape drawing mechanism of the apparatus, whereby read/write of data becomes feasible.
In such magnetic tape cartridges, conventionally, a projection for stacking is formed on the upper surface of the cartridge casing of each magnetic tape cartridge and a recess for stacking is formed on the lower surface of the cartridge casing of each magnetic tape cartridge so that, when a plurality of magnetic tape cartridges are stacked, the recess for stacking on one magnetic tape cartridge is engaged with the projection for stacking on the upper magnetic tape cartridge, whereby the relative position between the upper and lower magnetic tape cartridges is fixed so that a plurality of magnetic tape cartridges can be transported in a stacked state.
Conventionally, the projection for stacking on the lower surface of the cartridge casing is generally in the form of a pair of protrusions which extend in the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus on opposite sides of the circular opening. This arrangement gives rise to a problem that the protrusions are apt to warp and when they warp, the protrusion on each magnetic tape cartridge cannot be stably engaged with the engagement recess of the lower magnetic tape cartridge when a plurality of magnetic tape cartridges are stacked, whereby the magnetic tape cartridges become shaky.
Further, there has been also a problem that the protrusions increase sliding friction when the magnetic tape cartridge is inserted into the recording and reproducing apparatus.
In the magnetic tape cartridge, locator holes for locating the magnetic tape cartridge with respect to the recording and reproducing apparatus are often provided in the bottom wall of the lower half of the cartridge casing. In such a case, bosses each provided with a locator hole extending through the boss are formed on the bottom wall of the lower half at its four corners together with bosses each provided with through holes through which a screw for fastening together the upper and lower halves of the cartridge casing is inserted.
Further, a tape draw-out opening through which the magnetic tape in the cartridge casing is drawn out is formed in the side wall of the cartridge casing near one corner thereof, and a taper leader member is removably held in a space open to the tape draw-out opening between the lower surface of the top wall of the upper half and the upper surface of the bottom wall of the lower half. Accordingly, the tape draw-out opening must be provided with a space for accommodating the tape leader member, a space through which the magnetic tape runs and a space through which a tape draw-out member on the recording and reproducing apparatus is given access to the tape leader member, which greatly limits the space near the tape draw-out opening in which bosses can be provided.
Further, since a circular rib which coaxially surrounds the reel is erected from the upper surface of the bottom wall of the lower half, the space near the tape draw-out opening in which bosses can be provided is further limited and accordingly, the bosses for the locator holes and the screw holes and the circular rib must be provided in contact with each other or close to each other.
However, when the bosses and the rib are formed in contact with each other or close to each other, the part is locally thickened, which makes it difficult to keep a sufficient dimensional accuracy and geometric accuracy of the locator holes when the cartridge casing is molded due to nonuniform cooling in the mold and difference in shrinkage factor. Further, the bosses, the holes and the rib become apt to lean.
Further, when there exists a part at which the wall thickness is extremely large as compared with other parts, there arises fear that sink marks and/or welding lines are generated on the inner surface of the locator hole and the locator hole is disabled from functioning as a locator.
Further, even in the case where the bosses and the rib are in contact with each other but are simply close to each other, the part of the wall of the mold between parts which are close to each other is less apt to be cooled as compared with other parts, and accordingly, it is difficult to keep a sufficient dimensional accuracy and geometric accuracy and the bosses, the holes and the rib become apt to lean.
Further, the magnetic tape cartridge is generally provided with a brake member which locks the reel not to rotate when the magnetic tape cartridge is not being used and a coiled spring which urges the brake member in the direction of the axis of rotation of the reel. Generally the cartridge casing is formed by plastic injection molding. The urging force of the coiled spring can deform outward the top wall and/or the bottom wall of the cartridge casing. When the top wall and/or the bottom wall of the cartridge casing is deformed outward, the cartridge casing can interfere with the reel to obstruct rotation of the reel, location of the magnetic tape cartridge with respect to the recording and reproducing apparatus can become infeasible and/or stacking of the magnetic tape cartridges can be adversely affected.
In order to overcome these problems, the cartridge casing has been formed by molding of a glass-fiber reinforced polycarbonate resin or the like so that the rigidity of the cartridge casing is increased and deformation of the cartridge casing is prevented.
However this approach has been disadvantageous in that the service life of the molds is shortened and wear of the bucket of the recording and reproducing apparatus is increased when the magnetic tape cartridge is loaded in or unloaded from the recording and reproducing apparatus. That is, use of glass fiber reinforcement is not preferred from these viewpoints.
Though the plastic injection molding is useful as a technique for accurately and efficiently forming products of a complicated shape, it gives rise to a problem that a gate mark is left on the surface of the products which can obstruct loading and unloading of the magnetic tape cartridge in and from the recording and reproducing apparatus and can be ground to produce plastic grindings during loading and unloading of the magnetic tape cartridge depending on the position of the gate mark.
When a desired magnetic tape cartridge is taken out from a library and loaded in a recording and reproducing apparatus by a chucking machine or when the magnetic tape cartridge is taken out from the recording and reproducing apparatus and returned to the library by the chucking machine, the gate mark sometimes obstructs stable chucking of the magnetic tape cartridge.
Though these problems can be avoided by disposing the gate in a recess of the surface of the cartridge casing, flow of the resin near the gate becomes low since the wall thickness near the gate becomes smaller due to existence of the recess. As a result, uneven packing of resin is generated near the gate, the end of the flow (e.g., side walls) can sink to deteriorate the dimensional accuracy and, at the worst, short molding can occur due to a poor packing pressure. Though these problems can be avoided by providing a plurality of gates, the approach adds to the cost and is not advantageous.
Further, the problems can be avoided by providing a tunnel gate or a side gate on a side wall or the like of the cartridge casing. However, this approach is disadvantageous in that the length of the path over which the resin flows is elongated and the dimensional accuracy of the product deteriorates.
Further, an arcuate rib is formed on each corner of the upper half to surround the reel. The ends of the arcuate rib merge into side walls of the upper half in tangential directions of the rib. Further, a corner of the upper half is often provided with a cutaway portion for preventing the magnetic tape cartridge from being inserted into the recording and reproducing apparatus in a wrong direction. The cutaway portion is formed, for instance, from the upper surface of the top wall of the upper half halfway of the height of the side wall by cutting the corner of the upper half in a shape like a triangle including a point near the intersection of the arcuate rib and the side wall.
In such a case, the part of the side wall near the intersection forms a recess at an upper part thereof while forming a thick wall portion at a lower portion thereof. The thick wall portion is cooled slower than the surrounding parts, which results in a sinkmark and/or lean in the part near the intersection and a step on the surface to be mated with the corresponding part of the lower half.
In view of the foregoing observations and description, a first object of the present invention is to provide a magnetic tape cartridge which can be stably stacked with other magnetic tape cartridges and is low in sliding friction when it is inserted into a recording and reproducing apparatus.
A second object of the present invention is to provide a magnetic tape cartridge which is provided with a boss provided with a locator hole extending through the boss and a boss provided with a through hole through which a screw for fastening together the upper and lower halves of the cartridge casing both formed near a tape draw-out opening through which the magnetic tape in the cartridge casing is drawn out, and is yet high both in dimensional accuracy and geometric accuracy of the locator hole.
A third object of the present invention is to provide a magnetic tape cartridge which is rigid enough to prevent expansion or deformation of the cartridge casing by urging force of the spring which urges the brake member and to ensure a sufficient clearance between the reel and the cartridge casing even if the cartridge casing is formed by molding of a plastic material without glass fiber.
A fourth object of the present invention is to provide a magnetic tape cartridge which can be formed by injection molding in such a manner that fine geometric properties can be formed with a high dimensional accuracy with one gate for each product disposed in a position where the gate mark does not interfere with loading and unloading the magnetic tape cartridge in and from the recording and reproducing apparatus and with chucking of the magnetic tape cartridge when the magnetic tape cartridge is taken out from and returned to a library.
A fifth object of the present invention is to provide a magnetic tape cartridge in which the aforesaid drawbacks inherent to the magnetic tape cartridge where an arcuate rib is formed on each corner of the cartridge casing to surround the reel so that their ends merge into side walls of the cartridge casing in tangential directions of the rib and a cutaway portion for preventing the magnetic tape cartridge from being inserted into the recording and reproducing apparatus in a wrong direction is formed on a corner of the cartridge casing can be effectively avoided.
The first object of the present invention can be accomplished by a magnetic tape cartridge in accordance with a first aspect of the present invention characterized in that island-like or point-like projections are provided at least three places of one of the upper and lower surfaces of the cartridge casing and recesses which are adapted to be engaged with the projections are provided on the other of the upper and lower surfaces of the cartridge casing so that, when a plurality of the magnetic tape cartridges are stacked, the projections and the recesses of the cartridge casings of magnetic tape cartridges which are just above and below each other are engaged with each other to keep the relative position between the magnetic tape cartridges.
That is, when the island-like or point-like projections are provided on the lower surface of the cartridge casing, the recesses are provided on the upper surface of the cartridge casing, and conversely, when the island-like or point-like projections are provided on the upper surface of the cartridge casing, the recesses are provided on the lower surface of the cartridge casing.
The expression xe2x80x9cisland-like projectionxe2x80x9d means a projection which is independent of its surroundings and has a small certain area and the expression xe2x80x9cpoint-like projectionxe2x80x9d means a projection which is independent of its surroundings and has a smaller certain area.
When the projections are provided on the lower surface of the cartridge casing and the recesses are provided on the upper surface of the cartridge casing, it is preferred that the height of the projections be slightly larger than the depth of the recesses so that a slight gap is formed between the lower surface of the upper magnetic tape cartridge and the upper surface of the lower magnetic tape cartridge when a plurality of magnetic tape cartridges stacked with the projections and the recesses engaged with each other.
Further, it is preferred that each of the projections be formed at a predetermined distance d from the edge of the cartridge casing.
Further, it is preferred that the height t of the projections be larger than the distance d.
Further, it is preferred that the projections be formed near the leading edge and the trailing edge of the cartridge casing with respect to the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus.
Further, it is preferred that the distance d of the projection from the leading edge or the trailing edge of the cartridge casing satisfies the condition t less than dxe2x89xa60.15 D, wherein t represents the height of each projection, and D represents the length of the cartridge casing as measured in the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus.
In the case where the projections are provided on the lower surface of the cartridge casing, it is preferred that the projections be formed outside the circular opening, formed in the lower surface of the cartridge casing at the center thereof, with respect to the direction perpendicular to the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus.
In the magnetic tape cartridge in accordance with the first aspect of the present invention, since the projections for holding the magnetic tape cartridges in place relative to each other, when a plurality of magnetic tape cartridges are stacked, are island-like or point-like and are very small in area, the sliding friction acting between the magnetic tape cartridge and the recording and reproducing apparatus can be reduced. Further, unlike the conventional magnetic tape cartridge where the projections are in the form of protrusions, a stack of the magnetic tape cartridges becoming shaky due to warpage of the projections can be avoided.
When the projections are formed near the leading edge and the trailing edge of the cartridge casing with respect to the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus, the magnetic tape cartridges are stabilized when they are stacked. In this case, when each of the projections is formed at a predetermined distance from the edge of the cartridge casing, damage on the projections when the magnetic tape cartridge is dropped can be suppressed.
In the case where the projections are provided on the lower surface of the cartridge casing, when the projections are formed outside the circular opening, formed in the lower surface of the cartridge casing at the center thereof, with respect to the direction perpendicular to the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus, the drive member of the apparatus can be prevented from interfering with the projections, and at the same time, the magnetic tape cartridges are more stabilized when they are stacked.
The second object of the present invention can be accomplished by a magnetic tape cartridge in accordance with a second aspect of the present invention characterized in that a first boss provided with a locator hole for locating the magnetic tape cartridge relative to a recording and reproducing apparatus when the magnetic tape cartridge is loaded in the recording and reproducing apparatus and a second boss provided with a through hole through which a screw for fastening together the upper and lower halves of the cartridge casing is inserted are erected in contact with each other or close to each other from the inner surface of the cartridge casing near a tape draw-out opening, and the wall thickness of the first boss is smaller than the wall thickness of the second boss.
In this case, it is preferred that the wall thickness of the first boss be in the range of 0.5 to 0.8 times the wall thickness of the second boss.
Further, in the case where a sliding door for opening and closing the tape draw-out opening is provided, it is preferred that the second boss be provided on the outer peripheral surface thereof with a flat surface which is in alignment with the inner edge of a sliding groove formed on the cartridge casing so that the sliding door slides on the groove.
In the case where an arcuate rib coaxially surrounding the reel is erected from the inner surface of the cartridge casing, it is preferred that the first and second bosses be apart from the rib.
In the magnetic tape cartridge in accordance with the second aspect of the present invention, since the first boss provided with the locator hole is smaller in wall thickness than the second boss provided with a through hole through which a screw for fastening together the upper and lower halves of the cartridge casing is inserted, the first boss is cooled faster than the second boss and accordingly the dimensional accuracy and the geometric accuracy of the locator hole can be more easily obtained.
When the second boss is provided on the outer peripheral surface thereof with a flat surface which is in alignment with the inner edge of the door sliding groove formed on the cartridge casing, the second boss can be formed at a sufficient distance from the first boss, and accordingly the dimensional accuracy and the geometric accuracy of the through hole can be more easily obtained and at the same time, lean of the locator hole can be prevented.
Further, in the case where an arcuate rib coaxially surrounding the reel is erected from the inner surface of the cartridge casing, the dimensional accuracy and the geometric accuracy of the through hole can be obtained by forming the first and second bosses apart from the rib.
In the case where a boss provided with a locator hole is erected from the inner surface of the lower half of the cartridge casing near a tape draw-out opening, it is preferred that the lower surface of the upper half of the cartridge casing be provided with a circular recess opposed to the boss. The circular recess can be used for locating the upper half relative to the lower half during assembly of the magnetic tape cartridge.
The third object of the present invention can be accomplished by a magnetic tape cartridge in accordance with a third aspect of the present invention characterized in that a pair of protrusions are provided on each of the lower surface of the top wall of the upper half of the cartridge casing and the upper surface of the bottom wall of the lower half of the cartridge casing to respectively extend along diagonal lines of the cartridge casing.
Each of the protrusions may be uniform in height substantially over its entire length. In this case, it is preferred that the protrusion is about 0.1 mm to 0.5 mm in height. Otherwise, the protrusion may become lower toward the side walls of the cartridge casing at a predetermined rate or stepwise.
By providing such protrusions, the cartridge casing can be rigid enough to prevent expansion or deformation of the cartridge casing by urging force of the spring which urges the brake member and to ensure a sufficient clearance between the reel and the cartridge casing even if the cartridge casing is formed by molding of a plastic material without glass fiber.
Instead of providing such protrusions, the top wall of the upper half of the cartridge casing and the bottom wall of the lower half of the cartridge casing may be formed so as to be thicker toward the center thereof.
The fourth object of the present invention can be accomplished by a magnetic tape cartridge in accordance with a fourth aspect of the present invention characterized in that a thick wall portion is formed in one of the top wall of the upper half of the cartridge casing and the bottom wall of the lower half of the same and a gate for injection molding is provided in a recess formed on the outer surface of the thick wall portion.
It is preferred that the thick wall portion be formed in the top wall of the upper half of the cartridge casing at the center thereof and the gate for injection molding be provided in a recess formed on the outer surface of the thick wall portion.
The gate may be provided in a recess formed on the outer surface of the upper half or the lower half for a purpose other than that for providing a gate.
By providing the gate in a recess, the problems that the gate mark left on the surface of the product obstructs loading and unloading of the magnetic tape cartridge in and from the recording and reproducing apparatus and the gate mark is ground to produce plastic grindings can be avoided. Further, by providing the gate in a recess formed on the outer surface of a thick wall portion, flow of the resin becomes more smooth, and especially when the gate is provided in a recess formed on the outer surface of a thick wall portion formed in the top wall of the upper half of the cartridge casing at the center thereof, the length of the path over which the resin flows during injection molding can be substantially uniform, and the thickness of the cartridge casing near the gate can be prevented from becoming thin even if the gate is formed in a recess.
In the case where a pair of locator holes for locating the magnetic tape cartridge with respect to the recording and reproducing apparatus are provided on the bottom surface of the lower half of the cartridge casing, the gate may be provided in a recess formed on the bottom surface of the lower half in a region surrounded by a straight center line which passes through the center of the bottom surface of the lower half in parallel to the straight line joining the locator holes and a pair of straight lines extending on the bottom surface of the lower half through the respective locator holes in perpendicular to the center line. In this case, especially when the gate is provided at substantially the same distance from the locator holes, the resin can be evenly supplied to both the locator holes from the gate and accordingly the locator holes can be formed at a high accuracy.
Further, in the case where the projections for stacking are provided on the bottom surface of the lower half, the gate may be provided in a region on the trailing side of the projections with respect to the direction of insertion of the magnetic tape cartridge into the recording and reproducing apparatus.
In this case, since the region is not brought into contact with the recording and reproducing apparatus when the magnetic tape cartridge is loaded in and unloaded from the recording and reproducing apparatus, the problems that the gate mark left on the surface of the product obstructs loading and unloading of the magnetic tape cartridge in and from the recording and reproducing apparatus and the gate mark is ground to produce plastic grindings can be avoided without forming a recess.
The fifth object of the present invention can be accomplished by a magnetic tape cartridge in accordance with a fifth aspect of the present invention comprising a cartridge casing formed by fixing together rectangular upper and lower halves, a single reel which is housed for rotation in the cartridge casing and around which a magnetic tape is wound, an arcuate rib which is formed on the cartridge casing to surround the reel and an end of which intersects a side wall of the upper half or the lower half to form a thick wall portion near the intersection of the end of the arcuate rib and the side wall, a cutaway portion, for preventing the magnetic tape cartridge from being inserted into the recording and reproducing apparatus in a wrong direction, formed on the outer surface of the upper half or the lower half at a corner thereof to extend from the upper surface of the upper half or the bottom surface of the lower half halfway of the height of the side wall in such a manner that it cuts the corner in a shape like a triangle including the vicinity of the intersections of the arcuate rib and the side walls and characterized in that a thickness reduction portion which makes the thickness of the side wall substantially uniform is formed on the back side of the side wall near the intersection.
By forming a thickness reduction portion on the part adjacent to the cutaway portion in the direction of height of the side wall, the difference in cooling rate can be substantially nullified near the intersection, whereby formation of a sinkmark and/or lean in the part near the intersection is prevented and formation of a step on the surface at which the upper and lower halves are mated is prevented.